In a device of this type, a motor provides energy to the engagement spring. Thereafter, the engagement spring gives a portion of its energy to the disengagement spring, and said transfer of energy requires the presence of various mechanical members, and in particular of a cam which needs to move out of the way after transferring energy so as to make subsequent operation of the disengagement spring possible.
These mechanical members have low efficiency and are subject to wear and to play, requiring adjustment and maintenance. It would be desirable to replace the mechanical transfer members by means which are free from wear and play.
Proposals have been made, in particular in the document DT 2 361 972 A1 to provide control in which the engagement spring transmits a portion of its energy to the disengagement spring by hydraulic means. However the embodiment proposed is complex and expensive.
An aim of the invention is to provide a control device in which all of the parts share a common axis of symmetry, thereby obtaining advantageous savings in implementation and in assembly.